The present invention relates to a method for storing and reproducing a radiation image utilizing a radiation image storage sheet and a radiation image storage device having a radiation image storage layer favorably employable for the radiation image storing and reproducing method.
As a method replacing a conventional radiography, a radiation image storing and reproducing method utilizing a stimulable phosphor was proposed, and is practically employed. The radiation image storing and reproducing method employs a radiation image storage panel (i.e., stimulable phosphor sheet) comprising a stimulable phosphor, and comprises the steps of causing the stimulable phosphor of the storage panel to absorb radiation energy having passed through an object or having radiated from an object; sequentially exciting the stimulable phosphor with an electromagnetic wave such as visible light or infrared rays (i.e., stimulating light) to release the radiation energy stored in the phosphor as light emission (i.e., stimulated emission); photoelectrically detecting the emitted light to obtain electric signals; and reproducing the radiation image of the object as a visible image from the electric signals. The p thus treated is subjected to a step for erasing a radiation energy remaining therein, and then stored for the next image storing and reproducing procedure. Thus, the radiation image storage panel can be repeatedly employed.
In the method, a radiation image is obtainable with a sufficient amount of information by apply a radiation to the object at a considerably smaller dose, as compared with a conventional radiography using a combination of a radiographic film and radiographic intensifying screen.
The radiation image storage panel has a basic structure comprising a support and a stimulable phosphor layer provided thereon. But, if the phosphor layer is self-supporting, the support may be omitted. On the free surface (surface not facing the short) of the phosphor layer, a transparent protective film is generally placed to keep the phosphor layer from chemical deterioration or physical damage.
The phosphor layer generally comprises a binder and stimulable phosphor particles dispersed therein, but it may consist of agglomerated phosphor without binder. The phosphor layer containing no binder can be formed by deposition process or firing process. Further, the layer comprising agglomerated phosphor soaked with a polymer is also known. In any types of phosphor layers, the stimulable phosphor releases a stimulated emission when excited with a stimulating light after having been exposed to a radiation such as X-rays. Accordingly, the radiation in the form of an image having passed through an object or radiated from an object is absorbed by the phosphor layer of the storage panel in proportion to the applied radiation dose, and a radiation image of the object is produced in the storage panel in the form of a latent radiation energy-stored image. The latent radiation energy-stored image can be released as stimulated emission by sequentially irradiating the panel with stimulating light. The stimulated emission is then photoelectrically detected to give electric signals, so as to reproduce a visible image from the electric signals.
Even in the radiation image storing and reproducing method described above, it is naturally desired that a radiation image is reproduced with a high sensitivity and with good quality (such as a high sharpness and good graininess). Therefore, it is preferred to employ a stimulable phosphor which can efficiently absorb a radiation energy which is applied to the phosphor and releases a high stimulated emission as quickly as possible when a stimulating light is applied.
Until now, a certain number of stimulable phosphors are proposed and some of the proposed stimulable phosphors have been practically employed. The conventional radiation image storing and reproducing method utilizes a system in which a stimulable phosphor absorbs a radiation energy transmitted from the object and then relieves a stimulated emission when a stimulating light is applied. It is not easy to produce or discover a phosphor which can efficiently absorb a radiation energy which is applied to the phosphor and then releases a desired high stimulated emission as quickly as possible when a stimulating light is applied.
For instance, a rare earth metal activated alkaline earth metal fluorohalide phosphor is well known as a stimulable phosphor which releases a stimulated emission efficiently. However, the fluorohalide phosphor is not satisfactory in the property absorbing a radiation energy when a radiation is applied to the phosphor. Moreover, it does not release the stimulated emission within a desirably short second after it receives the stimulating light. This indicates that the response time of the fluorohalide phosphor is not satisfactorily short.
The problem in the unsatisfactory response time can be solved by the use of a sensor system comprising a multiple number of sensor members such as a line sensor. However, the problem in the unsatisfactory absorption of the radiation energy has not been solved.
Japanese Patent Provisional Publication No. 55-12142 discloses stimulable ZnS phosphors, and Japanese Patent Provisional Publication No. 2-692 discloses an alkali earth metal sulfide phosphors. These stimulable phosphors are still unsatisfactory, as long as the efficiency in absorbing an applied radiation energy is concerned.
Japanese Patent Publication No. 6-31904 describes a radiation image storage panel comprising a stimulable phosphor which absorbs a radiation energy of X-rays and further absorbs a ultraviolet light in the wavelength region of 250 nm to 400 nm and a phosphor which absorbs a radiation having a wavelength of shorter than 250 nm and emits a ultraviolet light in the wavelength region of 250 to 400 nm. Both phosphors are incorporated into one layer or incorporated separately into two phosphor layers. The ultraviolet light-absorbing phosphor serves as an aid to supply the stimulable phosphor with a radiation energy by converting the radiation energy into a ultraviolet light which can be absorbed by the stimulable phosphor.
The present invention has an object to provide a new radiation image storing and reproducing method showing a high detection quantum efficiency.
Specifically, the invention has an object to provide a radiation image storing and reproducing method which gives a reproduced radiation image of a high quality at a relatively low radiation dose applied to the object such as a human being.
Further, the invention has an object to provide a radiation image storage device which gives a reproduced radiation image of a high quality at a relatively low radiation dose.
As a result of a series of studies on detection quantum efficiency (DQE) in the radiation image storing and reproducing method, the inventor has had an idea to employ two or more kinds of phosphors, one of which efficiently absorbs a radiation such as X-rays applied to the phosphor and releases a spontaneous light emission, and another or other of which efficiently absorbs the light emission and stores the light emission as a radiation energy which can be released in the form of a light why it is exposed to a stimulating light.
The inventor has further studied the above-described idea and attained to the present invention which has a variety of working systems and embodiments.
From one aspect, the present invention resides in a method (I) for storing and reproducing a radiation image which comprises the steps of:
placing a fluorescent sheet on a radiation image storage panel comprising a fluorescent layer and a radiation image storage layer in such manner that the fluorescent sheet is arranged adjacent to the image storage layer of the storage panel, so as to give a composite structure, the fluorescent sheet containing a phosphor which absorbs a radiation energy and emits a light of ultraviolet or visible region, the fluorescent layer of the storage panel containing a phosphor which absorbs a radiation energy and emits a light of ultraviolet or visible region, and the radiation image storage layer of the storage panel containing a phosphor which absorbs the light emitted by the phosphors of the fluorescent layer and the fluorescent sheet to store therein energy of the absorbed light and releases the stored energy in the form of a light upon irradiation with a light of visible or infrared region;
applying onto the composite structure on the side of the fluorescent sheet or the radiation image storage panel a radiation having penetrated through an object, a radiation having been emitted by an object, or a radiation having been scattered or diffracted by an object, so as to store energy of the applied radiation in the form of a latent image on the image storage layer of the storage panel;
separating the radiation image storage panel from the fluorescent sheet;
irradiating the image storage panel on the side of image storage layer with stimulating light in a visible or infrared region to excite the phosphor in the storage layer so that the energy stored in the storage layer in the form of a latent image is released in the form of a light;
collecting the light released from the storage layer by light-collecting means;
converting the collected light into a series of electric signals; and
producing an image corresponding to the latent image from the electric signals.
From another aspect, the invention resides in a method (II) for storing and reproducing a radiation image which comprises the steps of:
placing a radiation image storage panel between two fluorescent sheets so as to give a composite structure, each of the fluorescent sheets containing a phosphor which absorbs a radiation energy and emits a light of ultraviolet or visible region, and the radiation image storage panel containing a phosphor which absorbs the light emitted by the phosphors of the fluorescent sheets to store therein energy of the absorbed light and releases the stored energy in the form of a light upon irradiation with a light of visible or infrared region;
applying onto the composite structure on one side a radiation having penetrated through an object, a radiation having been emitted by an object, or a radiation having been scattered or diffracted by an object, so as to store energy of the applied radiation in the form of a latent image on the image storage panel;
separating the radiation image storage panel from the fluorescent sheets;
irradiating the image storage panel with stimulating light in a visible or infrared region to excite the phosphor in the storage panel so that the energy stored in the storage panel in the form of a latent image is released in the form of a light;
collecting the light released from the storage panel by light-collecting means;
converting the collected light into a series of electric signals; and
producing an image corresponding to the latent image from the electric signals.
From a further aspect, the invention resides in a method (III) for storing and reproducing a radiation image which comprises the steps of:
placing a radiation image storage panel on a fluorescent sheet so as to give a composite structure, the fluorescent sheet containing a phosphor which absorbs a radiation energy and emits a light of ultraviolet or visible region, and the radiation image storage panel containing a phosphor which absorbs the light emitted by the phosphor of the fluorescent sheet to store therein energy of the absorbed light and releases the stored energy in the form of a light upon irradiation with a light of visible or infrared region;
applying onto the composite structure on one side a radiation having penetrated through an object, a radiation having been emitted by an object, or a radiation having been scattered or diffracted by an object, so as to store energy of the applied radiation in the form of a latent image on the image storage panel;
separating the radiation image storage panel from the fluorescent sheet;
irradiating the image storage panel with stimulating light in a visible or infrared region to excite the phosphor in the storage panel so that the energy stored in the storage panel in the form of a latent image is released in the form of a light;
collecting the light released from the storage panel by light-collecting means;
converting the collected light into a series of electric signals; and
producing an image corresponding to the latent image from the electric signals.
From a still further aspect, the invention resides in a method (IV) for storing and reproducing a radiation image which comprises the steps of:
providing a radiation image storage panel comprising a fluorescent layer and a radiation image storage layer, the fluorescent layer containing a phosphor which absorbs a radiation energy and emits a light of ultraviolet or visible region, and the radiation image storage layer containing a phosphor which absorbs the light emitted by the phosphor of the fluorescent layer to store therein energy of the absorbed light and releases the stored energy in the form of a light upon irradiation with a light of visible or infrared region;
applying onto the storage panel a radiation having penetrated through an object, a radiation having been emitted by an object, or a radiation having been scattered or diffracted by an object, so as to store energy of the applied radiation in the form of a latent image on the image storage layer of the storage panel;
irradiating the image storage panel on the side of image storage layer with stimulating light in a visible or infrared region to excite the phosphor in the storage layer so that the energy stored in the storage layer in the form of a latent image is released in the form of a light;
collecting the light released from the storage layer by light-collecting means;
converting the collected light into a series of electric signals; and
producing an image corresponding to the latent image from the electric signals.
From a still further aspect, the invention resides in a method (V) for storing and reproducing a radiation image which comprises the steps of:
providing a plurality of cassettes each of which has therein a fluorescent sheet on a front side thereof, fluorescent sheet containing a phosphor which absorbs a radiation energy and emits a light of ultraviolet or visible region and having a thickness differing from each other;
selecting one of the cassettes;
placing a radiation image storage panel in the selected cassette an a back side thereof, the radiation image storage panel containing a phosphor which absorbs the light emitted by the phosphor of the fluorescent layer to store therein energy of the absorbed light and releases the stored energy in the form of a light upon irradiation with a light of visible or infrared region;
applying onto the front side of the cassette a radiation having penetrated through an object, a radiation having been emitted by an object, or a radiation having been scattered or diffracted by an object, so as to store energy of the applied radiation in the form of a latent image on the image storage panel;
taking the image storage panel out of the cassette;
irradiating the image storage panel on the side with stimulating light in a visible or infrared region to excite the phosphor in the image storage panel so that the energy stored in the image storage panel in the form of a latent image is released in the form of a light;
collecting the light released from the image storage panel by light-collecting means;
converting the collected light into a series of electric signals; and
producing an image corresponding to the latent image from the electric signals.
From a still further aspect, the invention resides in an apparatus for storing and reproducing a radiation image utilizing a fluorescent sheet containing a phosphor which absorbs a radiation energy and emits a light of ultraviolet or visible region, and a radiation image storage panel containing a phosphor which absorbs the light emitted by the phosphor of the fluorescent layer to store therein energy of the absorbed light and releases the stored energy in the form of a light upon irradiation with a light of visible or infrared region, which comprises:
a housing having on outer surface thereof a plate with which an object is kept in contact;
the radiation image storage panel fixed within the housing in a position facing the plate;
the fluorescent sheet which is provided in the housing in a position facing the fixed image storage panel under such condition that the fluorescent sheet is able to move forward and backward in relation to the image storage sheet; and
a light-detecting means which is placed in the vicinity of the image storage panel and which is able to move into a space formed when the fluorescent sheet moves backward.
In the invention, the radiation employable for the radiation image reproduction means X-rays, xcex1-rays, xcex2-rays, xcex3-rays, ultraviolet rays, neutron-rays, and their analogue rays. The ultraviolet to visible wavelength region means a wavelength range of 200 nm to 600 nm, while the visible to infrared wavelength region means a wavelength range of 500 nm to 1,600 nm.